Wikipedia:Reference desk/Archives/Science/2016 May 3

= May 3 =

Energy of elementary particles and forces
Why is it that elementary particles and forces in their ground state keep going forever with whatever they are doing? What feeds the required energy to them?202.58.203.82 (talk) 02:10, 3 May 2016 (UTC)
 * You asked this question yesterday and it had responses. See: Reference desk/Science JoshMuirWikipedia (talk) 06:06, 3 May 2016 (UTC)
 * There's nothing to stop them.   D b f i r s   13:25, 3 May 2016 (UTC)
 * Thank you202.58.203.82 (talk) 04:10, 7 May 2016 (UTC)

Water-damaged tablet displays vertical bands of white
Days in a bin of rice haven't reversed the most visible damage. What is likely the cause of the vertical bands? Thank you. Imagine Reason (talk) 14:40, 3 May 2016 (UTC)


 * Have you tried asking at the Computing Reference Desk? -- Jayron 32 15:35, 3 May 2016 (UTC)


 * Sorry, I forgot. Imagine Reason (talk) 16:25, 3 May 2016 (UTC)


 * One guess: there's either still some water, or else residue of whatever was dissolved in the water, where the display cable plugs in (if you give us the model of the tablet we should be able to figure out if this is a possibility). If you can take it apart, you might try unplugging it and cleaning the contacts with a cotton swab and alcohol.  Of course, doing anything like this carries a risk of destroying it, so you might want a professional to do it. StuRat (talk) 15:46, 3 May 2016 (UTC)


 * It's the Lenovo S8-50. Imagine Reason (talk) 16:25, 3 May 2016 (UTC)


 * seems to say it lacks an output to an external monitor. Too bad, because that would help you to figure out where the problem lies (if the external monitor still had those lines, then the problem is in the graphics processor, if not, it's in the connection to the display).  Also, if the external monitor looked good, you could use it that way most of the time, and just live with the lines when you needed to use it where no external monitor was available. StuRat (talk) 16:47, 3 May 2016 (UTC)


 * Professional don't like to do it because tablets can be notoriously tricky to dissemble and resemble and most repair men are software orientated any way. If the whole screen is banded then that’s probable the graphics processor on the motherboard that needs cleaning. Don't use mentholated spirits but Isopropanol . Just the odd line on the screen though, is probable an address line on the screen shorting out (try it by pressing the screen gently in that edge spot). Same thing, clean edge of screen terminals with care. You have little to loose because the device has had it otherwise. Last thoughts, is it still under warranty? If it wasn’t submerged long enough to start sprouting barnacles, then you might be able to get it replaced free of charge. Get you data off first before parting company with it.--Aspro (talk) 16:10, 3 May 2016 (UTC)


 * The are multiple such lines of varying widths. They don't cover up the display and it's more apparent on the home screen than in at least one app, although the lines reappear at undetermined intervals. It's out of warranty I think and I doubt it got so small a soaking that they wouldn't notice it. As I said, it's obviously on the display. Imagine Reason (talk) 16:25, 3 May 2016 (UTC)


 * Vertical stripes are caused by some of the addressing circuitry or wiring leading from the graphics chip to the display...or within the display itself. If one or two low-order bits of the address lines are broken or shorted, you get this effect.  Sadly, that probably won't help you in getting it fixed. SteveBaker (talk) 17:46, 3 May 2016 (UTC)


 * Now that you have identified the device, I can link to a video to show why a professional (unless he is being paid oodles of taxpayers money by the NSA or CIA) would not touch it, as it would cost you more than the current value of said tablet. Disassembly Lenovo S850 Observe what has to be done to remove case without damaging the circuitry. However, if you wish to persevere then notice that at about 6 minutes into the video he reattaches the screen via a little ribbon cable. This is more than likely were the problem lays regarding  your reported  symptoms. With the ribbon cable separated, an aerosol can of 'Contact Cleaner' might just do the trick. --Aspro (talk) 18:00, 3 May 2016 (UTC)


 * Agreed. It might be better to get a new one and just use this old one as a backup in case the primary goes down. StuRat (talk) 19:36, 3 May 2016 (UTC)
 * Please note that the S8-50 is not the same as the S850. Mine, the former, is an 8-inch tablet. Here's a teardown? Imagine Reason (talk) 23:09, 3 May 2016 (UTC)
 * Can't comment much on the S850 since it's a video and it's annoying to watch just to get an idea of what's involved but the S8-50 doesn't look that hard. I replaced the screen on my S4 Mini (not something I purchased but won) without AFAIK breaking anything and I'd never done anything similar before other than help a friend take off the back cover of their Nexus 4 to replace the batter. I think the S4 Mini was slightly easier than the S850 looks since it used more Philips screws and not much stick tape that needed to be heated (but the Nexus 4 did use similar); except that I bought the screen without the bezel partially due to confusion and removing the old screen did partially require this. (Although mostly the old screen got completely destroyed, however it was not working at all so it was no big loss.) But the S8-50 doesn't even seem to have that although you may have to be slightly carefully when using the guitar pick since if it's not using sticky tape or screws, I guess there are some clips which could be damage. Still it looks far easier than an iPhone for example. That said, as SteveBaker has said, it's difficult to be sure what's wrong. There's a slight chance fooling around with the ribbon cable may help, but it may also be the screen or something else is damaged. Not really sure how cleaning the SOC (who uses a seperate GPU on a tablet?) is supposed to help whatever was showing, it's very unlikely to. Given the uncertainty over whether replacing the screen will help, I'm not sure if it'll be worth it in your case unless you can find someone who'll let you return the screen even if it's not defective (if you only attach the ribbon cable there's a slight chance someone will be like that). But you could try taking it apart and cleaning everything as it sounds like it'll be of very limited utility anyway.  Nil Einne (talk) 07:48, 4 May 2016 (UTC)

possible earth-like planets orbiting single stars
Are there any known possible earth-like planets that orbit single stars? — Preceding unsigned comment added by 24.207.71.235 (talk) 18:15, 3 May 2016 (UTC)
 * What are known possible earth-like planets? Robert McClenon (talk) 18:21, 3 May 2016 (UTC)
 * Are our methods of detecting extrasolar planets sufficiently precise that we can detect earth-sized planets? If so, are they sufficiently precise that we can detect earth-sized planets if the system also includes a Jupiter-sized planet?  Robert McClenon (talk) 18:21, 3 May 2016 (UTC)
 * Earth analog. HenryFlower 18:24, 3 May 2016 (UTC)

Earth-sized planets orbiting single stars.24.207.71.235 (talk) 20:00, 3 May 2016 (UTC)
 * Coincidentally I was just reading about this recent discovery of exoplanets believed to be between half and double the Earth's mass. AndrewWTaylor (talk) 20:20, 3 May 2016 (UTC)


 * Since you seem to not have read the article Henry helpfully linked above, I did it for you and pulled out the link to our list of potentially habitable exoplanets. --71.110.8.102 (talk) 21:07, 3 May 2016 (UTC)
 * Thank you. That list provides enough information that if a reader thinks that particular planetary circumstances are not suitable for Earth-like life, that reader can eliminate those planets.  For instance, some theorists think that planets in the habitable zones of M-type stars are not good life candidates, because of the high likelihood of tidal lock.  Of course, different theories as to habitability differ.  As the article on Drake equation points out, the Drake equation has zero degrees of freedom with only a single known habitable planet.  In any case, we are here.  Robert McClenon (talk) 16:56, 4 May 2016 (UTC)


 * That claim about tidally locked planets seems fishy to me. What if the planet has a big moon, and tidal-locks to the moon?  Or what if the moon is the inhabited body, and tidal-locks to the planet? Or for that matter, what if the moon simply orbits the planet and reflects sunlight onto the "dark cool side" of the planet, permitting photosynthetic life and moderating the temperature?  Or, on a different tack -- these planets have really short orbital periods.  So what if one has a highly elliptical orbit, so that the star ends up nearly 90 degrees away from the hot side during the incoming and outgoing phases of the orbit, providing a different sort of day? Wnt (talk) 01:53, 6 May 2016 (UTC)

why does wind feel colder than still air
If movement creates heat, then shouldnt moving air feel warmer than still air? — Preceding unsigned comment added by 24.207.71.235 (talk) 18:18, 3 May 2016 (UTC)
 * See wind chill. -- Jayron 32 18:24, 3 May 2016 (UTC)
 * (ec)Read Wind chill and it should become clear. The cold wind is pulling heat from you faster than still, cold air would. And I can tell you from experience in the American Midwest that minus-20 with calm air is a lot more tolerable than minus-20 with significant wind. ←Baseball Bugs What's up, Doc? carrots→ 18:26, 3 May 2016 (UTC)


 * From memory, each knot of wind only increases the topographic temperature by 0.007 degrees centigrade (think that the right order of magnitude). Therefore, air currents blows away the envelope of warmed air around the body (clothes mitigate this as they 'trap' this body-warmed air). Eject from a plane at Mach 2 however, then obviously one will suffer a momentary heat-pulse until one slows down a bit.--Aspro (talk) 18:32, 3 May 2016 (UTC)


 * I know of 2 reasons:


 * 1) Wind blows away the warm air envelope around your body, as Aspro mentioned above. This obviously only applies when the air the replaces the air blown away is cooler.


 * 2) That same air envelope is also moist. Blowing that away and replacing it with drier air then causes moisture on your skin to evaporate more quickly, causing increased evaporative cooling.  This obviously only applies when the air that replaces the air blown away is drier.


 * So, if the outside air is hotter and moister than the air envelope around you, then wind won't help to cool you down. In fact, it will heat you up more quickly, just like a convection oven cooks food more quickly than a normal oven (but if it's that hot and humid out you will overheat in any case, it's just a matter of when). StuRat (talk) 19:09, 3 May 2016 (UTC)


 * The simplest explanation is that air currents (convection) of any sort speeds heat transfer, always. That is, moving air speeds the rate at which heat either moves into or out of an object.  The laws of thermodynamics don't particularly care which direction the heat is moving.  If the air is cooler than the object, wind will cool off the object faster than still air.  If the air is warmer than the object (as in a convection oven) it will heat the object faster.  It's that simple.  -- Jayron 32 19:31, 3 May 2016 (UTC)


 * I've experienced 115+ degrees Fahrenheit in Las Vegas in July...I truly remember the breeze making things worse...the other odd thing is that you're sweating like mad but have no idea that you are as the evaporation is instantaneous...68.48.241.158 (talk) 19:33, 3 May 2016 (UTC)


 * It's a good thing you were sweating so much, as your body temp would otherwise quickly match or surpass the environmental temp, and you would die. (I believe people in such a situation do quickly die once they run out of water.) StuRat (talk) 19:40, 3 May 2016 (UTC)
 * Anhidrosis indeed. DMacks (talk) 21:38, 3 May 2016 (UTC)

Unidentified lichen (?)
Is this a lichen? Which? This was photographed in northern Georgia (country). Etan J. Tal(talk) 21:33, 3 May 2016 (UTC)


 * Yes, it's lichen. Try Physcia and see where that takes you. Richard Avery (talk) 21:54, 3 May 2016 (UTC)


 * Yep, lichen ID can be very hard though! Our only non-redlink article in the Physcia genus is Physcia_stellaris, which does look a lot like OP's photo, as well as the lichen I see all over my pecans in TX. Here is a nice lichen ID resource from the USFS, including several good external links. SemanticMantis (talk) 22:02, 3 May 2016 (UTC)


 * I'm lichen this answer. StuRat (talk) 02:33, 4 May 2016 (UTC)

Name a technical device.
The lenses of modern photo and video cameras change focal distance. What is the name for this principle, or this type of lens?

I also have another question. Do lenses exist that change the focal distance electronically via voltage application?

Thanks, --AboutFace 22 (talk) 22:56, 3 May 2016 (UTC)


 * for your first question, see Zoom lens. For your second question - you need to be more specific. Do you mean electrically driven zoom mechanism, do you mean "Digital zoom" where the lens does not actually move but the image is magnified and cropped electronically, or do you mean an actual optical element changing its curvature or refraction coefficient when voltage is applied across it? --Dr Dima (talk) 23:03, 3 May 2016 (UTC)
 * Actually, a zoom lens is one for which the focal length can be held constant while changing only the magnification. The original question asked for a lens whose focal length can change - technically, no single lens made of rigid glass or plastic is able to do that - but a lens group can.  In common parlance, photographers often say a "lens" when they actually mean several lenses - rather, "a large, engineered optical device containing several pieces of glass and a special mechanism to hold those glass pieces in a carefully-calibrated optical alignment."  We have an article on photographic lens design; and I can't recommend this book highly enough, Applied Photographic Optics - though it is regrettably quite expensive!
 * We also have an excellent article, History of photographic lens design. It is possible that our OP is looking for a specific lens type - like the 3-element Abbe lens grouping; or the Cooke triplet, or one of the more famous complex lens groupings that, for example, allow a focal length change while maintaining a very precisely carefully controlled field-of-view.
 * Lenses that are non-rigid have been studied for a very long time - ever since people started building optics. The human eye lens works in that fashion; and many optical engineers have tried to mimic that machine - but there are no commercially-available flexible-lens technologies today, electronically-actuated or otherwise, that can compete with the performance of rigid-glass lens mechanisms.  Nimur (talk) 02:06, 4 May 2016 (UTC)
 * I think you might be wrong about your first statement Numur, magnification IS the angle of view IS the "focal length", a zoom lens is called something like 55mm-105mm, meaning that you can vary it's focal length from 55mm all the way to 105mm, this changes the magnification and the angle of view and the focal length, it's all essentially the same thing. Vespine (talk) 02:14, 4 May 2016 (UTC)
 * As described below ... there are multiple focal lengths because modern systems have multiple elements. Permit me to admit my guilt - I am participating in abuse of terminology as much as anybody else.  Nimur (talk) 06:32, 4 May 2016 (UTC)
 * If you mean the latter - an optical element which will change its properties when voltage (electric field) is applied to it - you may want to read electro-optic effect, Pockels effect, and Kerr effect. Kerr effect, in particular, is used in femtosecond laser optics; but I am unaware of any use of these effects to change focal lengths of photographic or video lenses. --Dr Dima (talk) 23:17, 3 May 2016 (UTC)
 * Focal length is the principle, I'm not sure if that's synonymous with "focal distance", or if you mean something slightly different. A lens with a fixed focal length can still have a focus ring to change the distance at which it will achieve focus, it can also have an aperture which will govern the depth of field. Vespine (talk) 02:11, 4 May 2016 (UTC)
 * The term is used and abused badly in various contexts. Modern optical systems have multiple different focal lengths.  Nimur (talk) 02:14, 4 May 2016 (UTC)
 *  allow a focal length change while maintaining a very precisely carefully controlled field-of-view. you need to explain this to me please. I've studied photography and am an amateur astronomer and I'm struggling to figure out how to change focal length while maintaining a uniform field of view. Vespine (talk) 02:19, 4 May 2016 (UTC)
 * from the Focal length article: Focal length (f) and field of view (FOV) of a lens are inversely proportional. For a standard rectilinear lens, FOV = 2 arctan x/2f, where x is the diagonal of the film. So unless the camera system dynamically changes the sensor size, i don't see how you can alter the FL without also altering the FOV. Vespine (talk) 02:23, 4 May 2016 (UTC)
 * The effective focal length of the entire optical system can differ from, e.g., the back flange focal length. Ultimately, this is purely an issue of nomenclature and conventions when describing lens systems that contain multiple lenses.  I am in otherwise complete agreement with your statements: focal length and magnification and field of view are all intrinsically related - but the issue stems from the fact that each individual lens in a multi-element group may have a distinct focal length.  Modern devices can change total effective focal length, while holding back-plane focal length constant, using complex gearing systems to adjust the relative position of each element.  Nimur (talk) 06:27, 4 May 2016 (UTC)

Thank you very much. A lot to digest for me now. For some reason I thought "zoom" is a process but the lens could have a different name. A very fascinating topic. Thank you. --AboutFace 22 (talk) 16:18, 4 May 2016 (UTC)

@Dr. Dima, I actually meant changing the curvature of the lens with applied voltage. Although I consider myself technically adept with considerable math background, the optics is the farthest from my regular interests. Now I have an opportunity to hone some concepts and definitions. Again I am very grateful for all contributions. --AboutFace 22 (talk) 16:37, 4 May 2016 (UTC)


 * photonic metamaterials in theory should be able to change refractive index under some sort of control - but I don't know if anything like that has been invented yet. Wnt (talk) 02:03, 6 May 2016 (UTC)